Residual Strength Of Remolded Loess In Ring Shear Tests

With the characteristics of the largest number, most widely distributed and strongesthazards, loess landslides have become one of the most serious geological disasters in ourcountry including landslide, collapse, debris flow. As a result of landslide, the strengthparameters of slip zone are described by residual strength in most cases. The residualstrength is the minimum strength or final strength in drained shear tests, direct shearapparatus and triaxial apparatus cannot achieve the long displacement which residual strengthneeds,so as to they are not suitable as the residual strength research instrument, but with itsunique design ring shear apparatus can satisfy the resuest. So research on residual strengthby ring shear apparatus, and then evaluating slope stability and designing reinforcementschemes and designing anti-slide engineering and estimating the intensity of earthquakeliquefaction zone are meaningful.This paper carried out the ring shear tests by HJ-1type ring shear apparatu on remoldedloess collected from Cuishi brickkiln, Jingyang County. It explores the deformation andstrength characteristics of loess under different conditions (consolidation state, water content,dry density, the effective normal stress, shear mode and consolidation ratio), the mainconclusions are as follows:(1) Strength and deformation regularity of normal consolidated loessThe strength of the normal consolidated loess appears soften with the shear displacementincreasing, shear rate has little effect on peak strength and residual strength. Under the sameconditions, shear stress at the same shear displacement decreases with the increase ofmoisture content.The peak strength of loess increase with dry density, but the residualstrength is little affected by dry density, and softening becomes obvious with the decrease ofmoisture content and increase of dry density. The peak strength and residual strengthof normally consolidated remoulded loess increase with the effective normal stress, and thestrength of soils appears to softed after the first level loads, and increases slightly then soonreaches residual strength while second, third and fourth level load, the greater of effectivenormal stress, the less of shear displacement to achieve the residual strength.The deformation performance of normally consolidated loess is shear compression. Thesettlement deformation of specimens whose moisture content is low increases with the effective normal stress after the multilevel shear, but when moisture content of specimens ishigher than the plastic limit value, the settlement deformation is affected by water contentand thr effective normal stress.(2) Strength and deformation of over consolidated loessThe strength of the over consolidated loess appears soften with the shear displacementincreasing, with a same over consolidation ratio, shear rate has little effect on peak strengthand residual strength. Over consolidation ratio has little effect of on residual strength, thatis stress history means nothing to residual strength of over consolidated loessDeformation of over consolidated loess is smaller than normal consolidation loess. Overconsolidation ratio has a greater influence on the deformation of the soil, along with theincrease of over consolidation ratio, the deformation of over consolidated loess changes fromshear contraction into short dilatancy and shearing shrinkage, and appears dilatancy lastly.(3) Analysis of strength and engineering characteristics for soil in different conditionsMost of the peak strength index of normal consolidated loess is greater than its residualstrength index tested by ring shear apparatus,and this paper provides a proposed formulabetween peak and residual friction angle of Jingyang loess.The character of strain softening of normal consolidated loess and over consolidatedloess is analyzed by strain threshold, for normally consolidated loess and overconsolidated loess, the strain corresponding to the peak strength is greater than it to residualstrength, as well as the strain corresponding to the peak strength and residual strength of overconsolidated loess is not more than that of normally consolidated loess.The brittleness index of normal consolidated loess is low, and with the increase of theeffective normal stress, softening of the specimen goes into weaken. The strength ruckbildungof specimens with large dry density is obvious, the brittleness index decreases with theincrease of shear rateand moisture content.The ruckbildung of over consolidated loess is evident. The brittleness index of loess withlow water content increases with the increase of over consolidation ratio, but when themoisture content of loess slightly increased, the brittleness index decreases with the increaseof moisture content, this shows that the brittleness index of overconsolidated loess iscomprehensive effected by moisture content and over consolidation ratio.